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Discussion Starter · #1 ·
Theory and Practice of Land Cruiser Heating Anomolies.


OK, I'm new at this "internal compustion engine" concept, but my Cruiser runs hot at freeway speed.

My Setup:
'68 FJ40, stock straight 6,
stock-ish radiator (probably a replacement, but stock size)
electric fan mounted in front.
Temp guage is plumbed inline with the heater core, after water comes out of the head.

Been playing around with cooling- removed thermistat (please, I told you not to roll your eyes),
plumbed in a pressure guage, yes a pressure guage, to the coolant system.
7lb rad cap works fine and cycles fine, just like it says in the theory books. (7lb cap, not 14lb or more because that poor F engine has spit out 2, yes 2, freeze plugs.)
Straight water right now, no risk of freezing (gotta love these California winters. ha!). At the rate my radiator spring leaks and motor pops out freeze plugs, I can't afford coolant.


The situation:
Weather was nice, 60-65F today here. Around town it runs cold as ice, 120F if that. Get on the freeway, spin it at 3k rpm, heats up to 190 pretty quick, then creaps up toward 220F. I get scared, drop it down to 2500 rpm and let it cool down to 190ish, then back on. Get off the freeway, idling and temp falls real quick.

Before I pulled the thermistat, situation was identicle except engine would heat up faster because thermistat help water at 180F. So instead of rising 100 deg, it only went up 30 degrees before I'd get scared and back off.

Questions-
1) Does that 500 rpm between 2500 and 3k rpm really make that much difference? Shouldn't going faster down the hiway mean that more air is going thru the radiator and cool it down, at least enough to not heat up like that?

2) Once the weather warms up and I want to go to Death Valley again, am I going to overheat like crazy? Figure at idle right now, water runs 50 degrees hotter than ambient. Is there a linear heating / cooling ratio? (meaning if ambient air is 110, I'll run 160 at idle?)

3) I did a search on this here website before posting (a newbie who learns!) and found reference to spark plug gap and overheating. What in the heck does spark plug gap have to do with engine temp? Mixture and timing I can understand, but timing? Do you increase or decrease gap to run cooler? Please explain.


This turned into quite a long post.
-tom
 

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I read an article on overheating at freeway speeds not so long ago, and it talked about having a bad head gasket. Basically said that at freeway speeds, there were gases escaping into the coolant system, making it less effective, etc... Something to think about.

I haven't heard of the spark plug gap theory, but it seems to make since, much like timing. A larger gap will give you more spark at higher RPM (I believe that is the right direction) than a spark plug with a smaller gap, which will burn hotter.

It could just be that the radiator isn't cooling effectively and the added heat the engine produces at freeway speeds is not taken away because of that. In that case, the radiator gets no additional cooling benefit at the higher speeds.

Cool Cruisers of texas has a 4 row radiator for $199 (last I checked)

Good luck
 

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i have the same problem, i just deal with it, aka pullover let it blow its top, cool down and continue on. It has done it with 2 motors now, 327 (used), and 350 (just broken in).

i never understood why it happens either.

I would reccomend runnign coolant. It prevents the water from boiling which is a very bad thing - pressure goes up as well as temp
 

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Sounds to me like the fan is blocking the air or you run a big bumper or something that is diverting the air....(winch or something) either that or the air can't get out of the engine compartment fast enough....try raising the the hood in the rear or remove some inner wells....make sure you have no leaks and 7 lbs isn't much and blowing freeze plugs is interesting as mine never did that.....
 

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:rolleyes: (just cause...lol)

Have a winch out front? Higher mount, like above the frame rails? They can act as a wing and direct air over your hood at higher speeds. If it's on there, remove it and experiment.

Stock clutch/solid fan AND the electric pusher? Remove the pusher - it might also be redirecting air at higher speeds, hindering instead of helping. Electric fans are inefficient as pushers as well.

The temp at the block will be much more accurate than in the heater core line....IMO, might relocate.
 

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1.) Is the electric fan you have designed to go in front of the radiator pushing the air through or behind the radiator pulling the air??

2) There is a product I believe made by redline oil that is called super cool that reduces the boiling point of the water.

3) The higher the lb rating on the cap the lower the boiling point is under pressure, meaning with a a 14lb cap the boiling point of the water is approx 20 degrees higher than at atmospheric pressure. Fix the freeze plug problem and run a higher pressure cap..

4) Do you have a recovery system to collect the liquid that is released when the caps opens...

5) If this doesnt work contact me. I represent a company that makes an after market safety cooling system that is used primarily on motorhomes at this time, that when your cooling system reaches a predetermined unsafe temp this kicks on and will cool a engine from 22o degrees to 180 in approximately 3 minutes. It will cycle with the cooling system continually keeping the engine cool at any speed.

5) Also try running a good synthetic additive in your oil. This will help to keep the oil cool, an oil cooler might also help..
 

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Check the timing. I had a FJ55 that would idle fine, cold infact, but as soon as you had it moving it would overheat eventually. The timing was way off(I had just purchased it).

Also, make sure the radiator is of sufficient capacity to cool the motor. It may be the right size, but may not have enough rows, fin density, etc. It could be restricted internally or even clogged fins preventing good airflow.

-Brett
 

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When flowing properly the cruiser motors are a marvel in cooling efficiency. Plum the temp gauge back in to the block. It will give you a more realistic view of what your motor is doing. Put the 13 lb cap back on and replace the freeze plugs. The 7lb unit is a bandaid.. Check your timing it does make a difference. get it back to about 8* btdc. Certain plugs do run hotter. It has more to do with where the electrode sits in relation to the combustion chamber than anythig else. But I seriously doubt that it makes any difference to you.

Have your radiator gone through. Have you pressure cleaned your coolant system anytime lately?

Put the thermostat back in it. But check it to make sure that it is working properly.

You do still have the mechanical fan, right?

Does the water in the coolant system look nice and clean everytime you end up seeing it? If it is staying clean then you probably do not have a blown head gasket. What does the oil look like?


As it stands right now you will overheat in a second in death Valley. So bring lots of water...
There is not a linear correlation of engine temps/ambient temps. If it is working properly you will not have any problems.

when you go to Death Valley give me a ring. I'll come out in my 72..
 

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Jason M said:
When flowing properly the cruiser motors are a marvel in cooling efficiency.
or a marvel in energy inefiecency :flipoff2: the only reason they don't tend overheat is that the block weighs a hell of alot & can absorb the heat the engine only makes @ the amazing 120hp. radiators are installed as a safety measure. :D

all kidding aside, you need to check your commpression to make sure you don't have a dead cylinder & deffinately check for the blown head gasket by looking for exhaust bubbles in the coolant. have your radiator cleaned by a proffesional radiator shop or buy a new one. this is in addition to all the other things above.
 

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Discussion Starter · #10 ·
Let me update you on the condition of the engine:

I broke #5 piston outside Baker on the way to the desert and had to tow it home.

Fix: I replaced the one piston, a new set of rings (#3 piston also had a broken ring) and rod bearings and slapped it back together. #5 hole had pretty bad scoring, an indentation really, and thus I'm quite sure it's not getting much compression on that one.

Just want her to hold together for one more year. Next winter she gets a motor/tranny transplant. (Haven't decided what yet.)

To clarify: the water temp guage sender is mounted on the head in a brass Tee, just where the coolant comes out, so water is flowing past it. This seems to give a more accurate, faster read of water temp. Did you mean put the temp sender actually on the block? Where?

Nothing in front of the radiator except the fan, no winch, lite bar, etc.. Fan is a pusher because it won't fit behind the rad. I shifted the position of the rad to fit the onboard compressor. Mech fan won't fit either..

I'll try these things and report back:
fiddle around with the timing again,
replace the thermistat,
bump back up to a 14 lb cap (I carry 3 spare freeze plugs now anyway ;)
put coolant in it again
try to relocate the elec fan

Thank you to my fellow CruiserHeads,
-tom
 

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LandCroozer said:
Let me update you on the condition of the engine:

I broke #5 piston outside Baker on the way to the desert and had to tow it home.

To clarify: the water temp guage sender is mounted on the head in a brass Tee, just where the coolant comes out, so water is flowing past it. This seems to give a more accurate, faster read of water temp. Did you mean put the temp sender actually on the block? Where?

Fan is a pusher because it won't fit behind the rad. I shifted the position of the rad to fit the onboard compressor. Mech fan won't fit either..

I'll try these things and report back:
fiddle around with the timing again,
replace the thermistat,
bump back up to a 14 lb cap (I carry 3 spare freeze plugs now anyway ;)
put coolant in it again
try to relocate the elec fan

Thank you to my fellow CruiserHeads,
-tom

Broke #5 piston???
or just broken rings?

The temp sender should be fine where it sounds like it is.

Pull off the OBA and put the rad in it's intended location. And put a shroud back on it. Then run the stock mech fan.
Would you rather it overheated or you had OBA?


That being said I don't think that it is the pusher fan. Much over 30 mph the fan is useless. I suspect that you are having problems because of the 7 lb cap and the low compression in #5. Do a compression check to find out what is actually going on in the motor. Check timing.
 

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Yup, I agree with the above... I ran an F motor that was slightly built with the stock fan and radiator for several years. Even with a spring over and 35" tires. I never had an overheating problem, and it can easily get over 100 here near Weed CA. I could crawl around the mountains in blistering heat all day, and take the freeway home w/o the temp ever getting past the first notch on the dash guage. I ended up breaking the fan into little pieces because of a busted engine mount, and still had no overheating problems. Cruisers will run pretty cold because of the enormous radiator design (for their HP)

I would do as they said above, get the shroud and mech fan back on and ditch the pusher electric and OBA (mine is mounted to the firewall). With a good head gasket, proper thermistat and cap, you should be fine. Check your distributor to make sure that you have the right one (vacuum retard or advance) and that it is working properly. The engine could run hot at hight RPM if the timing is too lean as well.

Good luck!
 

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I think we are all over analyzing this a little too much. Unless there is some freak occurance here, I'm about 95% sure it's something simple. Bad thermostat, radiator, radiator cap, loss of pressure, or a clog in the system. I've run a number of F and 2F engines on less than one cyl, with timing in all sorts of configurations and have never had problems unless it was something simple. I would start there then move into the "more advanced" theories later.
 

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Discussion Starter · #14 ·
More Detail of Piston 5- (skip if you don't care)
The top compression ring shattered into little bits. These little bits broke thru the top of the piston out of the land and pounded into the top of the piston against the head. The little bits of ring are about the size of grains of rice; There are 4-5 left still in the piston top. The #2 comp ring was fractured into a few pieces and siezed in its land. It was a combination of these two things that wore against the wall and gave the nice sized divit.

As an aside-

The piston walls are 40 over, the crank mains and rod bearings are 40 under. This motor can't be rebuilt any more. It's got 2 mismatched pistons in it (I did one, the PO must have done another). The motor has been overheated BADLY 4 times by me alone. I'm talking violent boil over till there was no water left, pegged the temp guage. (twice when the plugs spit out, once when I had a leak in the hose and my water squirted out, and another time I just wasn't watching the temp guage- no idea what happened) I've run it out of oil a few times (it leaks _really_ badly and sometimes I don't overfill it enough; get on a decline and 0 psi.) Plus god knows what the ******* PO did to it before I got it. He had the oil filter line held in with, I'm not kidding, JB Weld and duct tape.

It's junk.

Before I pull it and toss it in the river, if it runs at all I'm going to throw a brick on the gas pedal and let it blow. I'll pull the fenders and vidcam it and post it here.. :) Hopefully something cool will fly out of the block and hit the neighbors cat that pees on my tires..

I just want it to last for a few more Hollister runs till a motor swap is possible.

I'm not sure, but I believe the current term is Bootie Fab..
-t
 
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